In situ combustion using iron catalysts



as-as United States Patent 3,087,540 IN SITU COMBUSTKON USING IRON CATALYSTS Harry W. Parker, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed July 20, 1959, Ser. No. 828,027 17 Claims. (Cl. 166--11) This invention relates to a process for the catalytic in situ combustion of carbonaceous strata. A specific aspect of the invention pertains to a process for depositing an iron-containing catalyst in carbonaceous strata.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery methods.

Recovery of hydrocarbons from carbonaceous strata, such as various types of oil and tar sands, porous and fractured coal veins, and other permeable carbonaceous deposits is a rather slow process and consumes an appreciable proportion of the carbonaceous material as fuel during the process. I have found that the in situ combustion process can be speeded up and the combustion temperature can be decreased so that a smaller proportion of the carbonaceous deposit is consumed in the process, thereby producing a greater amount of hydrocarbons and fuel gas from the deposit in a shorter period of time.

Accordingly, it is an object of the invention to provide an improved process for producing hydrocarbons and other fuel from a carbonaceous stratum by in situ combustion. Another object is to provide an in situ combustion process for producing a permeable carbonaceous stratum at a faster rate and with production of a greater proportion of the carbonaceous material present in the stratum. A further object is to provide a catalytic process for recovery of hydrocarbons by in situ combustion. It is also an object of the invention to provide a process for depositing an iron-containing catalyst in a carbonaceous stratum which avoids precipitation of iron compounds on their Way into the stratum so as to avoid plugging of the pores of the stratum. Other objects will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises injecting an 3,087,540 Patented Apr. 30, 1963 aqueous solution of a suitable iron compound into a selected section of a permeable carbonaceous stratum under non-precipitating conditions so as to impregnate the pores of the stratum with said compound; thereafter driving excess liquid out of the selected section by injecting into same a suitable flushing gas so as to leave adsorbed iron compound in the pores of the stratum; thereafter igniting the section of stratum and moving a combustion front therethru so as to produce hydrocarbons therefrom; and recovering the produced hydrocarbons. In this manner the iron compound deposit in the pores of the stratum lowers the temperature of combustion and the combustion front is moved thru the stratum at a faster rate than is possible in the absence of the iron compound.

Another broad aspect of the invention, applicable to strata containing connate Water having dissolved therein one or more salts which cause precipitation of the injected iron compound and plugging before it reaches all of the pores of the stratum to be impregnated, comprises displacing the water in the stratum by injecting the solution of iron-containing compound having added thereto a suitable sequestering or chelating agent which prevents precipitation of the iron compound; and after the iron compound is adsorbed in the pores of the stratum, displacing the excess liquid with air or other suitable drying gas to prepare the impregnated stratum for in situ combustion catalyzed by the iron-containing catalyst. It is also feasible to first drive the water out of the section of stratum to be impregnated with the catalyst and produced by in situ combustion, by injecting thereinto a suitable flushing fluid such as clear water or inert gas and then injecting the iron-containing solution also containing the sequestering or chelating agent.

A suitable sequestering or chelating agent comprises citric acid and its salts and polyaminopolycarboxylic acids and their water soluble salts, particularly, sodium and potassium, and sodium and potassium polyphosphates. The polyaminopolycarboxylic acids and their sodium and potassium salts are known in the trade as Versenes. The potassium and sodium polyphosphates are known as Calg-ons.

The preferred iron salt is ferric nitrate Fe(NO .9H O which is readily soluble in water up to more than 10 weight percent calculated as Fe. Other iron compounds comprise iron carbonate, iron chloride, iron carbonyl, and etc. When utilizing ferric nitrate, the impregnating solution preferably contains from 0.5 to 10 weight percent iron calculated as Fe O The amount of sequestering or chelating agent should be comparable or equivalent to the amount of iron compound in the solution.

The section of stratum to be produced may comprise the stratum between a central ignition well and a ring of surrounding wells, in which case the injection of solution is preferably effected thru the central ignition well with water, solution and air being produced thru the wells in the ring. After drying out, the ignition is initiated around the central well by any suitable means, such as by burning a fuel pack in the ignition well adjacent the stratum and driving a combustion zone into the stratum by direct or inverse drive in conventional manner. The combustion front is then driven thru the stratum by injecting combustion-supporting gas thru the wells in the ring (inverse drive). The produced hydrocarbons are recovered thru the central ignition well. Catalyst deposition does not increase the rate of propagation or lower combustion temperature with direct drive but it would probably allow operation under more difiicult conditions.

The section of stratum to be ignited and produced by in situ combustion may comprise the intervening stratum between a line ofignition wells and one or two parallel lines of Wells, preferably, two, i.e., one line on each side of the line of ignition wells. The solution may be injected thru the line of ignition wells, which is preferred, or thru the lines of offset wells until solution appears in the line(s) of wells opposite the wells being used as injection wells. After flushing out excess liquid, leaving iron compound in the pores of the intervening stratum as by air drive, combustion is then initiated along the line of ignition wells, preferably by igniting alternate wells in the line and injecting air thru the remaining wells so as to move the combustion front across the intervening strips of stratum between wells in the line. When the combustion zone is established completely along the line of wells, combustion fronts are then driven by direct or inverse driyle across the intervening strips to the lines of offset we s.

Tests have shown that iron compounds thus deposited in a carbonaceous stratum reduce the ignition and combustion temperatures and also accelerate the fire propagation rate. By reducing the combustion temperature, substantially more oil or other hydrocarbon material may be produced from a given reservoir because of hundreds of-thousands or millions of tons of rock in the reservoir are heated to a lower temperature, thereby requiring less fuel consumption than with a higher temperature. Since the temperature of combustion is reduced as much as about 70 to 100 F. by the use of iron catalyst, the saving in fuel and increase in production of hydrocarbons from a reservoir represents a substantial economic advantage. The process of the invention not only produces more oil but does so in a shorter period of time than without the use of iron catalyst.

To illustrate the effects of the invention, a tar sand was produced with and without added iron catalyst to determine the temperature of combustion and the rate of movement of the combustion front thru the sand. It was found that the iron catalyst increased the rate of movement of the combustion front thru the sand by about percent and decreased the combustion temperature at least 70 F. Of course, inverse air injection was used.

In other tests, a tar sand from the Bellamy, Missouri, area was burned clean of carbonaceous material and found to contain 1.7 weight percent iron. A portion of this clean sand was impregnated with an aqueous solution of ferric nitrate made by dissolving 65 gr. Fe(NO .9H O in 100 ml. water. The impregnated sand was dried and the nitrate decomposed by heating. The effect of the unimpregnated and impregnated sands on the oxidation of propane in air was determined by packing the sand samples in a glass tube 2.83 cm. ID. The sand was heated while passing air containing 10.3 volume percent propane therethru at a flow rate of 181 standard cu. ft. per hour per square foot of cross section of sand. It was found that the temperature required to consume 50% of the oxygen was reduced from 1160 to 980 F. by increasing the iron content of the sand from 1.7 to 4.0 weight percent.

Other tar sands were analyzed for iron content and it was found that the iron content ranged from .36 to 1.7 (Bellamy sand). Monogas, Venezuela, tar sand had an iron content of 0.7 weight percent while that from the Sulfur, Oklahoma, area had 0.36 weight percent iron. Two sands had an iron content of 1.5 and 1.7 weight percent, respectively. It is reasonable to assume that the improvement in catalytic effect of a given deposit of iron in a sand will be better in sands of low initial iron content.

During the in situ combustion phase of the process, the iron compound is probably decomposed or converted to iron oxide; however, the invention is not predicated upon any theory as to the form in which the iron exists at the time of its catalytic effect upon the combustion process.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing a permeable carbonaceous stratum containing water and penetrated by a pair of spaced apart wells by in situ combustion comprising passing a flushing gas thru said stratum between said wells to drive out water; thereafter injecting into the section of said stratum between said wells an aqueous solution of an iron compound under non-precipitating conditions; thereafter driving excess solution out of said section between said wells With a suitable flushing gas so as to leave adsorbed iron compound in the pores of said section; continuing the injection of said gas so as to dry out said stratum intermediate said wells; thereafter igniting said section adjacent one of said wells and injecting air into the ignited section so as to move a combustion front therethru toward the other of said wells so as to produce hydrocarbons therefrom whereby said iron compound lowers the temperature of combustion and causes movement of the combustion front thru said section at a faster rate than in the absence of said compound; and recovering the produced hydrocarbons from one of said wells.

2. The process of claim 1 wherein said compound is ferric nitrate in a concentration in the range of 0.5 to 10 weight percent (calculated as F6203).

3. The process of claim 1 wherein said solution is injected into a section of stratum between a central ignition well and a surrounding ring of wells, said igniting is effected in the area adjacent said ignition well, and the resulting combustion front is advanced toward the wells in said ring.

4. The process of claim 1 wherein said solution is injected thru a line of ignition wells to a parallel line of wells on each side of said line of ignition wells; and combustion fronts are driven from said line of ignition wells to each parallel line of Wells.

5. A process for producing a permeable carbonaceous stratum penetrated by a pair of spaced apart wells by in situ combustion which contains Water having salts dissolved therein, which comprises flushing said water out of the section of stratum between said Wells to be produced by displacing same with a suitable flushing fluid injected thru one of said wells and produced thru the other; thereafter injecting into said section through one of said wells an aqueous solution of ferric nitrate containing a chelating agent which prevents precipitation of Fe compounds, to displace said flushing agent; after Fe compound is adsorbed in the pores of said section, displacing excess solution with air injected thru one of said wells and drying out said section; thereafter igniting said section around one of said wells and continuing the injection of air so as to move a combustion front thru same toward the other of said wells; and recovering hydrocarbons produced by the combustion thru one of said wells.

6. The process of claim 5 where the flushing fluid is water relatively free of precipitating salts.

7. The process of claim 5 wherein the flushing fluid is a gas.

8. The process of claim 5 wherein the flushing fluid is air.

9. The process of claim 5 wherein said chelating agent is citric acid.

10. The process of claim 5 wherein said chelating agent is a member of the group polyaminopolycarboxylic acids and their water soluble salts.

11. The process of claim 5 wherein said chelating agent is sodium polyphosphate.

12. A process for depositing an iron-containing catalyst in a section of a permeable carbonaceous stratum between a pair of spaced apart wells therein to be produced by in situ combustion which section contains water having dissolved salt therein capable of precipitating iron compound which comprises flushing said water out of said section of stratum by displacing same with a suitable flushing fiuid injected thru one of said wells and produced thru the other; thereafter injecting thru one of said wells into said section an aqueous solution of an iron compound containing a chelating agent which prevents precipitation of Fe compounds, to displace said flushing agent thru the other well and after Fe compound is adsorbed in the pores of said section, displacing the excess solution between said wells with a drying gas and drying out said section, thereby depositing Fe compound in said section.

13. The process of claim 12 wherein said iron compound is ferric nitrate.

-14. -The process of claim 13 wherein the concentration of said ferric nitrate in said solution is in the range of 0.5 to 10 weight percent (calculated as Fe O 15. The process of claim 12 wherein said chelating agent comprises citric acid and said iron compound comprises ferric nitrate.

5 agent is a member of the group sodium and potassium polyphosphates.

References Cited in the file of this patent UNITED STATES PATENTS Frey Aug. 14, 1945 2,871,942 Garrison et a1. Feb. 3, 1959 

1. A PROCESS FOR PRODUCING A PERMEABLE CARBONACEOUS STRATUM CONTAINING WATER AND PENETRATED BY A PAIR OF SPACED APART WELLS BY IN SITU COMBUSTION COMPRISING PASSING A FLUSHING GAS THRU SAID STRATUM BETWEEN SAID WELLS TO DRIVE OUT WATER; THEREAFTER INJECTING INTO THE SECTION OF SAID STRATUM BETWEEN SAID WELLS AN AQUEOUS SOLUTION OF AN IRON COMPOUND UNDER NON-PRECIPITATING CONDITIONS; THEREAFTER DRIVING EXCESS SOLUTION OUT OF SAID SECTION BETWEEN SAID WELLS WITH A SUITABLE FLUSHING GAS SO AS TO LEAVE ADSORBED IRON COMPOUND IN THE PORES OF SAID SECTION; CONTINUING THE INJECTION OF SAID GAS SO AS TO DRY OUT SAID STRATUM INTERMEDIATE SAID WELLS; THEREAFTER IGNITING SAID SECTION ADJACENT ONE OF SAID WELLS AND INJECTING AIR INTO THE IGNITED SECTION SO AS TO MOVE A COMBUSTION FRONT THERETHRU TOWARD THE OTHER OF SAID WELLS SO AS TO PRODUCE HYDROCARBONS THEREFROM WHEREBY SAID IRON COMPOUND LOWERS THE TEMPERATURE OF COMBUSTION AND CAUSES MOVEMENT OF THE COMBUSTION FRONT THRU SAID SECTION AT A FASTER RATE THAN IN THE ABSENCE OF SAID COMPOUND; AND RECOVERING THE PRODUCED HYDROCARBONS FROM ONE OF SAID WELLS. 